SpringBoot进阶 - SpringBoot嵌入式Tomcat的自动配置原理
SpringSpringBoot大约 5 分钟
SpringBoot进阶 - SpringBoot嵌入式Tomcat的自动配置原理
1. 准备
我们知道SpringBoot的自动装配的秘密在org.springframework.boot.autoconfigure包下的spring.factories文件中，而嵌入Tomcat的原理就在这个文件中加载的一个配置类：org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration
@Configuration
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@ConditionalOnClass(ServletRequest.class)
@ConditionalOnWebApplication(type = Type.SERVLET)
@EnableConfigurationProperties(ServerProperties.class)
@Import({ ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class,
ServletWebServerFactoryConfiguration.EmbeddedTomcat.class,
ServletWebServerFactoryConfiguration.EmbeddedJetty.class,
ServletWebServerFactoryConfiguration.EmbeddedUndertow.class })
public class ServletWebServerFactoryAutoConfiguration {
@Bean
public ServletWebServerFactoryCustomizer servletWebServerFactoryCustomizer(
ServerProperties serverProperties) {
return new ServletWebServerFactoryCustomizer(serverProperties);
}
@Bean
@ConditionalOnClass(name = "org.apache.catalina.startup.Tomcat")
public TomcatServletWebServerFactoryCustomizer tomcatServletWebServerFactoryCustomizer(
ServerProperties serverProperties) {
return new TomcatServletWebServerFactoryCustomizer(serverProperties);
}
/**
* Registers a {@link WebServerFactoryCustomizerBeanPostProcessor}. Registered via
* {@link ImportBeanDefinitionRegistrar} for early registration.
*/
public static class BeanPostProcessorsRegistrar
implements ImportBeanDefinitionRegistrar, BeanFactoryAware {
private ConfigurableListableBeanFactory beanFactory;
@Override
public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
if (beanFactory instanceof ConfigurableListableBeanFactory) {
this.beanFactory = (ConfigurableListableBeanFactory) beanFactory;
}
}
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata,
BeanDefinitionRegistry registry) {
if (this.beanFactory == null) {
return;
}
registerSyntheticBeanIfMissing(registry,
"webServerFactoryCustomizerBeanPostProcessor",
WebServerFactoryCustomizerBeanPostProcessor.class);
registerSyntheticBeanIfMissing(registry,
"errorPageRegistrarBeanPostProcessor",
ErrorPageRegistrarBeanPostProcessor.class);
}
private void registerSyntheticBeanIfMissing(BeanDefinitionRegistry registry,
String name, Class<?> beanClass) {
if (ObjectUtils.isEmpty(
this.beanFactory.getBeanNamesForType(beanClass, true, false))) {
RootBeanDefinition beanDefinition = new RootBeanDefinition(beanClass);
beanDefinition.setSynthetic(true);
registry.registerBeanDefinition(name, beanDefinition);
}
}
}
}
1.1 相关注解
@AutoConfigureOrder这个注解是决定配置类的加载顺序的，当注解里的值越小越先加载，而Ordered.HIGHEST_PRECEDENCE的值是Integer.MIN_VALUE也就是说这个类肯定是最先加载的那一批@ConditionalOnXXX在之前的文章中已经无数次提到了，就不再阐述了@EnableConfigurationProperties开启ServerProperties类的属性值配置。而这个类里面包含的就是Web服务的配置@ConfigurationProperties(prefix = "server", ignoreUnknownFields = true) public class ServerProperties { private Integer port; private InetAddress address; @NestedConfigurationProperty private final ErrorProperties error = new ErrorProperties(); private Boolean useForwardHeaders; private String serverHeader; private int maxHttpHeaderSize = 0; // bytes private Duration connectionTimeout; @NestedConfigurationProperty private Ssl ssl; @NestedConfigurationProperty private final Compression compression = new Compression(); @NestedConfigurationProperty private final Http2 http2 = new Http2(); private final Servlet servlet = new Servlet(); private final Tomcat tomcat = new Tomcat(); private final Jetty jetty = new Jetty(); private final Undertow undertow = new Undertow(); }这个类的代码太多了，这里就不一一贴出来了，我们平常在
application.properties中配置的server.xxx就是这个类中属性
1.2 @Import引入4个类
1.2.1 BeanPostProcessorsRegistrar
public static class BeanPostProcessorsRegistrar
implements ImportBeanDefinitionRegistrar, BeanFactoryAware {
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata,
BeanDefinitionRegistry registry) {
if (this.beanFactory == null) {
return;
}
registerSyntheticBeanIfMissing(registry,
"webServerFactoryCustomizerBeanPostProcessor",
WebServerFactoryCustomizerBeanPostProcessor.class);
registerSyntheticBeanIfMissing(registry,
"errorPageRegistrarBeanPostProcessor",
ErrorPageRegistrarBeanPostProcessor.class);
}
private void registerSyntheticBeanIfMissing(BeanDefinitionRegistry registry,
String name, Class<?> beanClass) {
if (ObjectUtils.isEmpty(
this.beanFactory.getBeanNamesForType(beanClass, true, false))) {
RootBeanDefinition beanDefinition = new RootBeanDefinition(beanClass);
beanDefinition.setSynthetic(true);
registry.registerBeanDefinition(name, beanDefinition);
}
}
}
这个类注册了两个bean：
WebServerFactoryCustomizerBeanPostProcessor后置处理器获取bean
tomcatServletWebServerFactory的时候就会执行后置处理器的postProcessBeforeInitialization方法``ErrorPageRegistrarBeanPostProcessor`
registerSyntheticBeanIfMissing(registry,
"webServerFactoryCustomizerBeanPostProcessor",
WebServerFactoryCustomizerBeanPostProcessor.class);
registerSyntheticBeanIfMissing(registry,
"errorPageRegistrarBeanPostProcessor",
ErrorPageRegistrarBeanPostProcessor.class);
1.2.2 EmbeddedTomcat
@Configuration
@ConditionalOnClass({ Servlet.class, Tomcat.class, UpgradeProtocol.class })
@ConditionalOnMissingBean(value = ServletWebServerFactory.class, search = SearchStrategy.CURRENT)
public static class EmbeddedTomcat {
@Bean
public TomcatServletWebServerFactory tomcatServletWebServerFactory() {
return new TomcatServletWebServerFactory();
}
}
这个类会在存在Tomcat相关jar包时添加一个TomcatServletWebServerFactory bean
另外两个EmbeddedJetty，EmbeddedUndertow 类也是同样的，注册了对应ServletWebServerFactory。
该 ServletWebServerFactory 将会在createWebServer 是被使用
1.2.2.1 starter-web的默认容器
EmbeddedTomcat 中的 @ConditionalOnClass 表示，如果项目中存在tomcat 类，则该类会被加载配置。
而starter-web中默认配置的容器就是tomcat。如果需要使用其他容器，则移除该引用，改成其他引用即可
1.3 注入了两个类
ServletWebServerFactoryAutoConfiguration类还注入了两个类ServletWebServerFactoryCustomizer和TomcatServletWebServerFactoryCustomizer
现在前期准备工作已经做好了
2. 启动流程
2.1 启动入口 onRefresh
启动入口在ServletWebServerApplicationContext中的onRefresh方法
protected void onRefresh() {
super.onRefresh();
try {
createWebServer();
}
catch (Throwable ex) {
throw new ApplicationContextException("Unable to start web server", ex);
}
}
2.2 createWebServer启动Tomcat
Tomcat的启动就在createWebServer方法里面了
private void createWebServer() {
WebServer webServer = this.webServer;
ServletContext servletContext = getServletContext();
// 第一次访问的时候两个对象都为空
if (webServer == null && servletContext == null) {
// 使用工厂模式创建容器,因为内置的容器有很多种，不只是tomcat
ServletWebServerFactory factory = getWebServerFactory();
// getSelfInitializer() 环境配置,这是SpringContext 与ServletContext 进行通信的关键
// 启动WebServer(tomcat)
this.webServer = factory.getWebServer(getSelfInitializer());
}
else if (servletContext != null) {
try {
getSelfInitializer().onStartup(servletContext);
}
catch (ServletException ex) {
throw new ApplicationContextException("Cannot initialize servlet context",
ex);
}
}
initPropertySources();
}
2.2.1 获取 WebServerFactory
首先看一下getWebServerFactory
protected ServletWebServerFactory getWebServerFactory() {
// 这里获取的beanname就是上方注册的tomcatServletWebServerFactory了
String[] beanNames = getBeanFactory()
.getBeanNamesForType(ServletWebServerFactory.class);
if (beanNames.length == 0) {
throw new ApplicationContextException(
"Unable to start ServletWebServerApplicationContext due to missing "
+ "ServletWebServerFactory bean.");
}
if (beanNames.length > 1) {
throw new ApplicationContextException(
"Unable to start ServletWebServerApplicationContext due to multiple "
+ "ServletWebServerFactory beans : "
+ StringUtils.arrayToCommaDelimitedString(beanNames));
}
return getBeanFactory().getBean(beanNames[0], ServletWebServerFactory.class);
}
2.2.2 后置处理器 WebServerFactoryCustomizerBeanPostProcessor 执行定制器
准备环境里注册的bean现在出来一个了。注意，上方还注册了一个后置处理器WebServerFactoryCustomizerBeanPostProcessor，获取beantomcatServletWebServerFactory的时候就会执行后置处理器的postProcessBeforeInitialization方法
这个处理器的作用是获得所有定制器，然后执行定制器的方法
public Object postProcessBeforeInitialization(Object bean, String beanName)
throws BeansException {
if (bean instanceof WebServerFactory) {
postProcessBeforeInitialization((WebServerFactory) bean);
}
return bean;
}
private void postProcessBeforeInitialization(WebServerFactory webServerFactory) {
LambdaSafe
.callbacks(WebServerFactoryCustomizer.class, getCustomizers(),
webServerFactory)
.withLogger(WebServerFactoryCustomizerBeanPostProcessor.class)
.invoke((customizer) -> customizer.customize(webServerFactory));
}
private Collection<WebServerFactoryCustomizer<?>> getCustomizers() {
if (this.customizers == null) {
// Look up does not include the parent context
this.customizers = new ArrayList<>(getWebServerFactoryCustomizerBeans());
this.customizers.sort(AnnotationAwareOrderComparator.INSTANCE);
this.customizers = Collections.unmodifiableList(this.customizers);
}
return this.customizers;
}
@SuppressWarnings({ "unchecked", "rawtypes" })
private Collection<WebServerFactoryCustomizer<?>> getWebServerFactoryCustomizerBeans() {
return (Collection) this.beanFactory
.getBeansOfType(WebServerFactoryCustomizer.class, false, false).values();
}
2.2.3 getSelfInitializer() 绑定信息
返回一个lamda 函数,这是SpringContext 与ServletContext 进行通信的关键。简单描述逻辑为：
- SpringContext.setServletContext(ServletContext)
- ServletContext.setSpringContext(SpringContext)
这样双方都能够获取对方的完成信息。
private org.springframework.boot.web.servlet.ServletContextInitializer getSelfInitializer() {
return this::selfInitialize;
}
private void selfInitialize(ServletContext servletContext) throws ServletException {
prepareWebApplicationContext(servletContext);
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
ExistingWebApplicationScopes existingScopes = new ExistingWebApplicationScopes(
beanFactory);
WebApplicationContextUtils.registerWebApplicationScopes(beanFactory,
getServletContext());
existingScopes.restore();
WebApplicationContextUtils.registerEnvironmentBeans(beanFactory,
getServletContext());
for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
beans.onStartup(servletContext);
}
}
2.2.4 启动Tomcat
getWebServer->getTomcatWebServer->initialize->this.tomcat.start();
@Override
public WebServer getWebServer(ServletContextInitializer... initializers) {
Tomcat tomcat = new Tomcat();
File baseDir = (this.baseDirectory != null) ? this.baseDirectory
: createTempDir("tomcat");
tomcat.setBaseDir(baseDir.getAbsolutePath());
Connector connector = new Connector(this.protocol);
tomcat.getService().addConnector(connector);
customizeConnector(connector);
tomcat.setConnector(connector);
tomcat.getHost().setAutoDeploy(false);
configureEngine(tomcat.getEngine());
for (Connector additionalConnector : this.additionalTomcatConnectors) {
tomcat.getService().addConnector(additionalConnector);
}
prepareContext(tomcat.getHost(), initializers);
return getTomcatWebServer(tomcat);
}
protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) {
return new TomcatWebServer(tomcat, getPort() >= 0);
}
public TomcatWebServer(Tomcat tomcat, boolean autoStart) {
Assert.notNull(tomcat, "Tomcat Server must not be null");
this.tomcat = tomcat;
this.autoStart = autoStart;
initialize();
}
private void initialize() throws WebServerException {
TomcatWebServer.logger
.info("Tomcat initialized with port(s): " + getPortsDescription(false));
synchronized (this.monitor) {
try {
addInstanceIdToEngineName();
Context context = findContext();
context.addLifecycleListener((event) -> {
if (context.equals(event.getSource())
&& Lifecycle.START_EVENT.equals(event.getType())) {
// Remove service connectors so that protocol binding doesn't
// happen when the service is started.
removeServiceConnectors();
}
});
// Start the server to trigger initialization listeners
this.tomcat.start();
// We can re-throw failure exception directly in the main thread
rethrowDeferredStartupExceptions();
try {
ContextBindings.bindClassLoader(context, context.getNamingToken(),
getClass().getClassLoader());
}
catch (NamingException ex) {
// Naming is not enabled. Continue
}
// Unlike Jetty, all Tomcat threads are daemon threads. We create a
// blocking non-daemon to stop immediate shutdown
startDaemonAwaitThread();
}
catch (Exception ex) {
throw new WebServerException("Unable to start embedded Tomcat", ex);
}
}
}
3. 总结
核心主要还是依赖于springboot的自动配置。项目启动的过程中，扫描classpath下的meta-inf/spring.factories，实例化工厂对象tomcatServletWebServerFactory，在调用run()方法的时候完成tomcat对象的创建，环境设置和启动，从而实现tomcat容器的自动化处理。
SpringApplication --> run-->createContext-->context.refersh-->onRefresh-->createWebServer
参考文章
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